The present invention relates to a cleaning device for use in an image forming apparatus and, more particularly, to a cleaning device for removing developer from a photosensitive drum after an electrostatic latent image is developed and a developer image is transferred to a copying paper sheet.
An image forming apparatus, particularly an electronic copying apparatus, has an image forming body or photosensitive drum. An electrostatic latent image is formed on the drum and is then developed into a visible image with developer. The visible image is then transferred to a copying paper sheet. Thereafter, the residual developer remaining on the drum is removed therefrom; that is, the drum is cleaned and made ready to form another electrostatic latent image.
Various devices for cleaning photosensitive drums are known and used in practice. One of them has a rotary fur brush which is brought into contact with a photosensitive drum and which is rotated to remove the developer from the drum. Another known cleaning device has an elastic rubber blade which is moved in contact with the periphery of a photosensitive drum to scrape the remaining developer therefrom.
The photosensitive drum comprises a metal cylinder and a photosensitive layer formed on the outer circumferential surface of the cylinder. The photosensitive layer may be a selenium layer vapor-deposited on the outer circumferential surface of the cylinder. Alternatively, it may be formed by coating onto the outer circumferential surface of the cylinder a paint consisting of a resin and cadmium sulfide powder or zinc oxide powder dispersed in the resin. Further, it may be an organic photoconductive layer.
The developer used may be either a one-component developer consisting of toner particles and magnetic particles capsulated in the toner particles or a two-component developer comprising a mixture of toner particles and carrier particles.
A cleaning device is chosen and used according to the type of photosensitive layer used and the kind of developer used.
The known cleaning devices have drawbacks to be described hereinafter. A cleaning device with a fur brush cannot completely remove residual developer from a photosensitive drum when the developer particles are strongly attracted to the photosensitive layer of the drum by an electrostatic force. Cleaning is therefore inadequately performed, particularly when the residual developer is of a one-component type.
A cleaning device with an elastic rubber blade may damage the photosensitive layer of a photosensitive drum, since its blade is strongly pressed against the photosensitive layer. A selenium layer, in particular, may be scratched and may subsequently fail to form a good electrostatic latent image. A compression force of 1 to 2 g/mm is required to press the blade against the selenium layer. If a force less than the above force is applied to the selenium layer, a sufficient cleaning effect cannot be obtained. However, if the photosensitive drum is coated with a protective film such as a polyester film, it is possible to press the blade against the polyester film with a force of 5 to 7 g/mm. Since the force is increased, an improved cleaning effect can be obtained. However, when a photosensitive drum having such a protective layer thereon is used, a complex PIP method must be used to form an electrostatic latent image, unlike the xerographic copying process.